The present invention relates to ultrasonic horns. More particularly, the present invention relates to mounting an ultrasonic horn.
In ultrasonic welding (sometimes referred to as xe2x80x9cacoustic weldingxe2x80x9d), two parts to be joined (typically thermoplastic parts) are placed directly below a tool called an ultrasonic xe2x80x9chornxe2x80x9d for delivering vibratory energy. These parts (or xe2x80x9cworkpiecesxe2x80x9d) are constrained between the horn and an anvil. The horn transfers energy to the welded part by expanding and contracting with the application of ultrasonic energy, typically from between approximately 20,000 hertz to approximately 40,000 hertz. An ultrasonic type vibratory welding system basically comprises an electrical generating means, an electrical ultrasonic converter for converting electrical energy into vibratory energy, the horn for delivering the vibratory energy into the weld zone, and an assembly for applying a static force to the workpieces so as to hold the workpiece in forced contact with the tool. The energy is imparted from the tool to the workpiece at a selected wavelength, frequency, and amplitude. The ultrasonic horn is an acoustical tool made of, for example, aluminum or titanium that transfers the mechanical vibratory energy to the part.
One type of ultrasonic welding is continuous ultrasonic welding. This type of ultrasonic welding is typically used for sealing fabrics and films, or other workpieces which can be formed into a xe2x80x9cwebxe2x80x9d and fed through the welding apparatus. In continuous welding, the ultrasonic horn is typically stationary and the part is moved beneath it. One type of continuous ultrasonic welding uses a rotationally fixed bar horn and a rotationally fixed anvil surface. The workpiece is pulled between the bar horn and the anvil. The horn typically extends longitudinally towards the workpiece and the vibrations travel axially along the horn into the workpiece. In another type of continuous ultrasonic welding, the horn is a rotary type which is cylindrical and rotates about a longitudinal axis. The input vibration is in the axial direction of the horn and the output vibration is in the radial direction of the horn. The horn is placed close to an anvil which typically is also able to rotate so that the workpiece to be welded (or bonded) passes between the cylindrical surfaces at a linear velocity which substantially equals the tangential velocity of the cylindrical surfaces. This type of ultrasonic welding system is described in U.S. Pat. No. 5,976,316, incorporated by reference in its entirety herein.
The juxtaposition of the anvil to the horn allowed a static force to be provided to the workpiece, allowing the transmission of the ultrasonic energy to the workpiece. This static force was typically maintained by providing a pinching force to the workpiece from a force application system (e.g., using a fluid hydraulic system) which forced the horn radially towards the longitudinal axis of the anvil. The problem with this method of securing the workpiece was that when the workpiece being welded became extremely thin, or contained holes, the horn and the anvil could physically contact each other. When the horn contacted the anvil, a large spike in energy consumption occurred through the system, similar to an electrical short circuit. As throughput speeds of the workpiece were increased, the level of energy introduced through the horn was also increased, causing the frequency of the surges of energy which occurred during contact of the horn and anvil to exponentially increase. These high spikes of energy forced the machine into an overload condition causing it to shut down as well as potentially causing holes or brittle spots to be generated in the product. Thus, the amount of energy which could be introduced through the ultrasonic horn was limited in order to prevent the machine from entering into an overload condition. Consequently, the throughput speed of the workpiece or product had to be reduced to allow enough energy to be transferred to the workpiece to generate an adequate weld. In short, the process became inefficient and caused product damage when the horn and anvil contacted one another.
To remedy this problem, ultrasonic welding systems were developed which maintained a gap between the anvil and the horn. This gap was typically narrower than the thickness of the workpiece. The necessity to provide a pinching (or holding) force on the product, while maintaining a separation between the horn and the anvil, required a large and stiff support structure for both the horn and anvil. The support structure was necessarily rigid, to maintain the angular position of both the horn and the anvil with respect to each other. Mis-aligning the surfaces of the horn and anvil caused poor welding and loss of product. Similarly, attempting to adjust the distance of the gap in this type of system allowed an unacceptable level of movement to be introduced into the system, once again causing mis-adjustment of the surfaces of the horn and anvil. It is desirable, therefore, to provide a way to mount an ultrasonic horn next to an anvil so that a gap is maintained between the horn and the anvil, while maintaining the angular position of the horn with respect to the anvil, without requiring an overly large support structure.
The invention includes an apparatus comprising an ultrasonic horn. The horn is mounted to a support structure and includes a first mounting surface. An anvil is mounted to the support structure and spaced from the ultrasonic horn. The anvil has a first bearer surface. A bearer assembly supportably links the first mounting surface to the first bearer surface.
Another aspect of the invention includes a method for mounting an ultrasonic welding horn comprising securing the ultrasonic horn to a support structure. The horn has a welding surface and a first mounting surface. An anvil having a pressing surface and a first bearing surface is disposed such that the pressing surface is proximate to the welding surface. The welding surface and the pressing surface are biased towards each other. A linkage structure links the first bearing surface to the first mounting surface so as to prevent the pressing surface and the welding surface from coming into contact.